Light-emitting device and method for manufacturing same

ABSTRACT

Disclosed is a light-emitting device comprising a light-emitting element ( 10 ) composed of a gallium nitride compound semiconductor having an emission peak wavelength of not less than 430 nm; a molded body ( 40 ) provided with a recessed portion having a bottom surface on which the light-emitting element ( 10 ) is mounted and a lateral surface; and a sealing member ( 50 ) containing an epoxy resin including a triazine derivative epoxy resin, or a silicon-containing resin. The molded body ( 40 ) is obtained by using a cured product of a thermosetting epoxy resin composition essentially containing an epoxy resin including a triazine derivative epoxy resin, and has a reflectance of not less than 70% at the wavelengths of not less than 430 nm.

TECHNICAL FIELD

This invention relates to a light-emitting device for use as luminaires,displays, mobile phone backlights, moving picture illuminating auxiliarylight sources, and other general commercial light sources, a method forpreparing the same, a molded part, and a sealing member.

BACKGROUND ART

Surface mount light-emitting devices using light-emitting elementsfeature a small size, a good power efficiency, and light emission ofbrilliant color. The light-emitting elements eliminate the risk of lampfailures since they are semiconductor elements. They are alsocharacterized by improved initial drive performance and resistance tovibration and repeated turn-on and off. Because of these improvedproperties, light-emitting devices using light-emitting elements such aslight-emitting diodes (LED) and laser diodes (LD) are utilized as lightsources in varying applications. Recently, light-emitting elements havemarked a rapid advance toward higher outputs.

For the surface mount light-emitting devices, thermoplastic resins suchas liquid crystal polymers, polyphenylene sulfide (PPS) and nylon areoften used as molded parts due to ease of mass-scale production.

On the other hand, epoxy resins are used in sealing members forprotecting the light-emitting elements from moisture, dust andcontaminants (see, for example, Patent Reference 1: JP 3512732, PatentReference 2: JP-A 2001-234032, and Patent Reference 3: JP-A2002-302533).

Also silicone resins are used as the output of light-emitting elementsis increased.

However, prior art thermoplastic resins used as moldings in surfacemount light-emitting devices are less resistant to light due to theinclusion of an aromatic component within the molecule although they areresistant to heat. Also, since hydroxyl groups or other groups forimproving adhesion are absent at molecular ends, the resins exhibit pooradhesion to leads and sealing members. In particular, sealing membersusing silicone resins lack long-term reliability since they show adrastic drop in adhesion to molded parts using thermoplastic resins, ascompared with sealing members using epoxy resins.

Epoxy resins are used as sealing members, but not as molded parts inleadframe type surface mount devices because of their difficulty tomold.

Also, light-emitting elements of gallium nitride compound semiconductorcapable of blue emission produce higher outputs than light-emittingelements capable of red emission and also generate more amounts of heat.Thus, degradation of molded parts becomes a problem when light-emittingelements of blue emission are used.

Also, JP 2656336 (Patent Reference 4) describes an optical semiconductordevice wherein an encapsulating resin is a cured product of a B-stagedepoxy resin composition for optical semiconductor encapsulationcomprising an epoxy resin, a curing agent, and a cure accelerator,wherein the constituent components are uniformly mixed at a molecularlevel. It is described that the epoxy resin used herein is typically abisphenol A epoxy resin or bisphenol F epoxy resin, and triglycidylisocyanate or the like may also be used. In Example, triglycidylisocyanate is used and added in a small amount to a bisphenol type epoxyresin. As long as the present inventors have empirically studied, theB-staged epoxy resin composition for semiconductor encapsulation suffersfrom a problem of yellowing during long-term holding at hightemperatures.

JP 2656336 (Patent Reference 4) describes: “The epoxy resin compositionfor optical semiconductor encapsulation is advantageously used asencapsulants for light-sensing elements in compact disc players, linesensors and area sensors which are solid-state image sensors. Opticalsemiconductor devices in which light-sensing elements such assolid-state image sensors are encapsulated with such epoxy resincompositions for optical semiconductor encapsulation arehigh-performance products which form images free of fringes caused byoptical variations of the resin or black dots caused by foreignparticles in the encapsulating resin. Despite resin encapsulation, theyexhibit at least equivalent performance to ceramic packages.” It is thusunderstood that the encapsulating resin of this patent is used withlight-sensing elements, but not for the encapsulation of light-emittingelements.

In this regard, JP-A 2000-196151 (Patent Reference 5), JP-A 2003-224305(Patent Reference 6) and JP-A 2005-306952 (Patent Reference 7) refer tothe use of triazine derived epoxy resins in epoxy resin compositions forthe encapsulation of light-emitting elements. These epoxy resins,however, are not solid materials obtained by reacting a triazine derivedepoxy resin with an acid anhydride.

Known references relating to the present invention include the foregoingand Patent References 8 and 9 and Non-Patent Reference 1, listed below.

-   Patent Reference 1: JP 3512732-   Patent Reference 2: JP-A 2001-234032-   Patent Reference 3: JP-A 2002-302533-   Patent Reference 4: JP 2656336-   Patent Reference 5: JP-A 2000-196151-   Patent Reference 6: JP-A 2003-224305-   Patent Reference 7: JP-A 2005-306952-   Patent Reference 8: JP-A 2005-259972-   Patent Reference 9: JP-A 2006-156704-   Non-Patent Reference 1: Electronics Mount Technology, April 2004

DISCLOSURE OF THE INVENTION Problem to be Solved by the Invention

Accordingly, an object of the invention is to provide a light-emittingdevice using a molded part with improved heat resistance and lightresistance, and a method for preparing the same. Another object of theinvention is to provide a molded part and a sealing member for use in alight-emitting device.

Means for Solving the Problems

Making extensive investigations to solve the outstanding problems, theinventors have completed the present invention.

One aspect of the invention relates to a light-emitting devicecomprising a light-emitting element comprising a gallium nitridecompound semiconductor having an emission peak wavelength of 430 nm orlonger, and a molded part on which the light-emitting element isdisposed, the molded part using a cured product of a thermosetting epoxyresin composition comprising an epoxy resin including a triazine derivedepoxy resin. A light-emitting device with improved heat resistance andlight resistance is then provided even when the light-emitting elementcomprising a gallium nitride compound semiconductor is used.

The molded part is preferably a cured product of a thermosetting epoxyresin composition comprising (A) the epoxy resin including a triazinederived epoxy resin, and further comprising (B) an acid anhydride, (C)an antioxidant, (D) a curing catalyst, (E) a reflective member, and (F)an inorganic filler. This molded part has a good curability, improvedheat resistance and light resistance, and a satisfactory strength.

The thermosetting epoxy resin composition preferably comprises a solidmaterial in ground form obtained by melt mixing (A) the epoxy resinincluding a triazine derived epoxy resin with (B) an acid anhydride and(C) an antioxidant. The composition is then improved in flexuralstrength.

In this embodiment, the thermosetting epoxy resin composition preferablycomprises as a resin component a solid material in ground form obtainedby reacting a triazine derived epoxy resin with an acid anhydride insuch a proportion as to provide an epoxy group equivalent/acid anhydridegroup equivalent ratio from 0.6 to 2.0. More preferably, the reaction ofa triazine derived epoxy resin with an acid anhydride is effected in thepresence of an antioxidant; or the reaction of a triazine derived epoxyresin with an acid anhydride is effected in the presence of a curingcatalyst or a curing catalyst and an antioxidant. Also preferably, thethermosetting epoxy resin composition further comprises (E) a reflectivemember and (F) an inorganic filler.

The molded part preferably has a reflectance of at least 70% at 430 nmor longer. A light-emitting device featuring a high radiation efficiencyfrom the light-emitting element is then available.

Preferably the molded part has a recess with a bottom surface and a sidesurface, the light-emitting element is disposed on the bottom surface ofthe recess, and the light-emitting element is sealed with a sealingmember comprising an epoxy resin including a triazine derived epoxyresin or a silicon-containing resin. Then adhesion to the molded part issignificantly improved.

Another aspect of the invention relates to a light-emitting devicecomprising a light-emitting element having an emission peak wavelengthof 430 nm or longer, and a molded part on which the light-emittingelement is disposed, the molded part using a cured product of athermosetting epoxy resin composition comprising an epoxy resinincluding a triazine derived epoxy resin, an acid anhydride, areflective member, and a curing catalyst as essential components. A tolight-emitting device with improved heat resistance and light resistanceis then provided. Also in this embodiment, the epoxy resin including atriazine derived epoxy resin and the acid anhydride are preferablycompounded in the thermosetting epoxy resin composition as a solidmaterial in ground form obtained by reacting the triazine derived epoxyresin with the acid anhydride in such a proportion as to provide anepoxy group equivalent/acid anhydride group equivalent ratio from 0.6 to2.0. More preferably, the reaction of the triazine derived epoxy resinwith the acid anhydride is effected in the presence of an antioxidant;or the reaction of the triazine derived epoxy resin with the acidanhydride is effected in the presence of the curing catalyst or thecuring catalyst and an antioxidant, so that the curing catalyst is alsocompounded as the solid material in ground form.

A further aspect of the invention relates to a method for preparing alight-emitting device comprising the first step of mixing a solidmaterial in ground form obtained by melt mixing (A) an epoxy resinincluding a triazine derived epoxy resin with (B) an acid anhydride and(C) an antioxidant, with (A) a curing catalyst, (E) a reflective member,and (F) an inorganic filler, the second step of molding a thermosettingepoxy resin composition resulting from the first step in a mold withleads arranged in place by a transfer molding technique, and the thirdstep of disposing a light-emitting element on the leads on a curedproduct of the thermosetting epoxy resin composition resulting from thesecond step. Then a light-emitting device using a molded part in theform of a cured product of a thermosetting epoxy resin composition isreadily provided.

Also provided is a method for preparing a light-emitting devicecomprising the first step of mixing a solid material in ground formobtained by reacting a triazine derived epoxy resin with an acidanhydride in such a proportion as to provide an epoxy groupequivalent/acid anhydride group equivalent ratio from 0.6 to 2.0, with(D) a curing catalyst, (E) a reflective member, and (F) an inorganicfiller, the second step of molding a thermosetting epoxy resincomposition resulting from the first step in a mold with leads arrangedin place by a transfer molding technique, and the third step ofdisposing a light-emitting element on the leads on a cured product ofthe thermosetting epoxy resin composition resulting from the secondstep. Preferably in this embodiment, the reaction of the triazinederived epoxy resin with the acid anhydride is effected in the presenceof an antioxidant; or the reaction of the triazine derived epoxy resinwith the acid anhydride is effected in the presence of the curingcatalyst or the curing catalyst and an antioxidant, so that the curingcatalyst is also compounded as the solid material in ground form.

A still further aspect of the invention relates to a molded part for usein a light-emitting device, formed from a cured product of athermosetting epoxy resin composition comprising (A) an epoxy resinincluding a triazine derived epoxy resin, (B) an acid anhydride, (C) anantioxidant, (D) a curing catalyst, (E) a reflective member, and (F) aninorganic filler, components (A), (B) and (C) being compounded as asolid material in ground form obtained by melt mixing them. A moldedpart having improved heat resistance and light resistance is thenprovided.

A still further aspect of the invention relates to a sealing member foruse in a light-emitting device, formed from a cured product of athermosetting epoxy resin composition comprising (A) an epoxy resinincluding a triazine derived epoxy resin, (B) an acid anhydride, (C) anantioxidant, and (D) a curing catalyst, components (A), (B) and (C)being compounded as a solid material in ground form obtained by meltmixing them. A sealing member having improved heat resistance and lightresistance is then provided.

It is noted that photo-couplers are not encompassed within the scope ofthe invention and should be excluded.

Benefits of the Invention

The light-emitting device of the invention has improved heat resistance,light resistance and adhesion. The molded part on which a light-emittingelement is disposed is improved in curability, has a satisfactorystrength, and maintains heat resistance, light resistance and adhesionover a long term. The sealing member gives a cured product which isuniform and generates little variation in color.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a surface mountlight-emitting device according to one embodiment of the invention.

FIG. 2 is a schematic plan view of the surface mount light-emittingdevice of the embodiment.

FIG. 3 is a diagram showing a reflectance of a molded part according toanother embodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, the light-emitting device, molded part, sealing member and methodsfor preparing them are described by referring to their embodiments andexamples. It is understood that the invention is not limited to theembodiments and examples illustrated herein. A surface mountlight-emitting device according to one embodiment of the invention isdescribed with reference to the figures. FIG. 1 is a schematiccross-sectional view of a surface mount light-emitting device accordingto one embodiment of the invention. FIG. 2 is a schematic plan view ofthe surface mount light-emitting device of this embodiment. FIG. 1 is aschematic cross-sectional view taken along lines I-I in FIG. 2.

The light-emitting device 100 comprises a light-emitting element 10comprising a gallium nitride compound semiconductor having an emissionpeak wavelength of 430 nm or longer, and a molded part 40 on which thelight-emitting element 10 is disposed. The molded part 40 preferablyuses a cured product of a thermosetting epoxy resin compositioncomprising (A) an epoxy resin including a triazine derived epoxy resin,(B) an acid anhydride, (C) an antioxidant, (D) a curing catalyst, (E) areflective member, and (F) an inorganic filler. The molded part 40 hasfirst and second leads 20 and 30. The molded part 40 has a recess with abottom surface and a side surface, and the light-emitting element 10 isdisposed on the bottom surface of the recess. The light-emitting element10 has a pair of positive and negative electrodes, which areelectrically connected to the first and second leads 20 and 30 via wiresegments 60. The light-emitting element 10 is encapsulated with asealing member 50. The sealing member 50 is preferably formed of anepoxy resin including a triazine derived epoxy resin or asilicon-containing resin selected from among flexible and rigid siliconeresins, a rigid silicone resin, an epoxy-modified silicone resin, amodified silicone resin alone or a mixture of two or more becauseadhesion to the molded part 40 is then enhanced. Notably, encapsulationwith another epoxy resin or urethane resin is possible. The sealingmember 50 contains a phosphor 70 for converting the wavelength ofemission from the light-emitting element 10. The molded recessed part 40prepared using a mold or the like has such a high reflectance as toreduce the transmission of light into the bottom and side surfaces ofthe recess in the molded part 40 and to increase the release of lighttoward the front surface.

The molded part 40 is selected to have a high reflection efficiency at430 nm or longer since the light-emitting element 10 used has anemission peak wavelength of 430 nm or longer. Then the majority of lightemitted by the light-emitting element 10 is not absorbed in the moldedpart 40, but released to the exterior, leading to a high radiantefficiency from the light-emitting element 10. Inversely, if a moldedpart 40 having a low reflectance is used, the majority of light emittedby the light-emitting element 10 is absorbed in the molded part 40,whereby degradation of the molded part 40 is accelerated.

Molded Part

The molded part 40 used herein is a cured product of a thermosettingepoxy resin composition comprising (A) an epoxy resin including atriazine derived epoxy resin, (B) an acid anhydride, (C) an antioxidant,(D) a curing catalyst, (E) a reflective member, and (F) an inorganicfiller. The respective components are described below.

A. Epoxy Resin

Component (A) is an epoxy resin which contains a triazine derived epoxyresin.

A-1: Triazine Derived Epoxy Resin

The triazine derived epoxy resin is effective for restraining a curedproduct of a thermosetting epoxy resin composition from yellowing andfor establishing a semiconductor light-emitting device with littledegradation with time. The triazine derived epoxy resin is preferably a1,3,5-triazine nucleus derived epoxy resin. In particular, an epoxyresin having isocyanurate rings has excellent light resistance andelectrical insulation, and should preferably have a divalent, morepreferably trivalent epoxy group per isocyanurate ring. Specifically,tris(2,3-epoxypropyl) isocyanurate, tris(α-methylglycidyl) isocyanurateor the like may be used.

The triazine derived epoxy resin preferably has a softening point of 90to 125° C. It is noted that those resins having hydrogenated triazinerings are excluded from the triazine derived epoxy resin.

A-2: Hydrogenated Epoxy Resin

A hydrogenated epoxy resin (A-2) may be used in combination with thetriazine derived epoxy resin. The hydrogenated epoxy resin is preferablyan epoxy resin obtained by hydrogenating an aromatic epoxy resin, andmore preferably an epoxy resin having the following general formula (1).

Herein, R¹ and R² which may be the same or different is a hydrogen atom,methyl group or cyclohexyl group, and n is an integer of 0 to 20.

It is noted that the hydrogenated epoxy resin (A-2) preferably has asoftening point of 70 to 100° C.

A-3: Other Epoxy Resin

Also, if necessary, an epoxy resin (A-3) other than the foregoing (A-1)and (A-2) may be used in combination in an amount below a certain levelas long as this does not compromise the effect of the invention.Exemplary epoxy resins include bisphenol A type epoxy resins, bisphenolF type epoxy resins, biphenol type epoxy resins such as3,3′,5,5′-tetramethyl-4,4′-biphenol type epoxy resins and 4,4′-biphenoltype epoxy resins, phenol novolac type epoxy resins, cresol novolac typeepoxy resins, bisphenol A novolac type epoxy resins, naphthalene dioltype epoxy resins, trisphenylol methane type epoxy resins,tetrakisphenylol ethane type epoxy resins, and epoxy resins obtainedthrough hydrogenation of aromatic rings in phenol dicyclopentadienenovolac type epoxy resins.

It is noted that the other epoxy resin (A-3) preferably has a softeningpoint of 70 to 100° C.

The epoxy resin as component (A) is the triazine derived epoxy resin(A-1) optionally in admixture with the hydrogenated epoxy resin (A-2)and other epoxy resin (A-3). Components (A-1) and (A-2) are preferablyused in such a proportion as to provide a weight ratio (A-1):(A-2) inthe range from 10:0 to 2:8, specifically from 8:2 to 2:8, and morespecifically from 7:3 to 3:7. Too high a ratio of hydrogenated epoxyresin (A-2) may lead to a drop of heat resistance and light resistance.Also, component (A-3) is preferably admixed in a proportion of up to 30%by weight and more preferably up to 10% by weight, based on the totalweight of epoxy resins.

B. Acid Anhydride

Component (B) is an acid anhydride which serves as a curing agent. Itshould preferably be non-aromatic and free of a carbon-carbon doublebond in order to provide light resistance. Exemplary acid anhydridesinclude hexahydrophthalic anhydride, methylhexahydrophthalic anhydride,trialkyltetrahydrophthalic anhydride, and hydrogenated methylnadicanhydride, with the methylhexahydrophthalic anhydride being preferred.These acid anhydride curing agents may be used alone or in admixture oftwo or more.

The acid anhydride curing agent is preferably to compounded in an amountto provide 0.5 to 2.0 equivalents and more preferably 0.7 to 1.5equivalents of acid anhydride per equivalent of the epoxy resin. Lessthan 0.5 equivalent may result in under-curing and a loss ofreliability. If the amount is more than 2.0 equivalents, the unreactedcuring agent may be left in the cured product to adversely affect themoisture resistance thereof.

In this regard, where only the triazine derived epoxy resin (A-1) isused as component (A), the preferred amount of the acid anhydride curingagent compounded is such that 0.6 to 2.0 equivalents, more preferably1.0 to 2.0 equivalents, and even more preferably 1.2 to 1.6 equivalentsof acid anhydride groups are available per equivalent of epoxy groups inthe triazine derived epoxy resin. Less than 0.6 equivalent may result inunder-curing and a loss of reliability. If the amount is more than 2.0equivalents, the unreacted curing agent may be left in the cured productto adversely affect the moisture resistance thereof.

C. Antioxidant

Component (C) is an antioxidant which may be selected from phenol,phosphorus and sulfur based antioxidants. Examples of suitableantioxidants are described below.

Examples of phenol based antioxidants include 2,6-di-t-butyl-p-cresol,butylated hydroxyanisole, 2,6-di-t-butyl-p-ethylphenol,stearyl-β-(3,5-di-t-butyl-4-hydroxyphenyl)propionate,2,2′-methylenebis(4-methyl-6-t-butylphenol),4,4′-butylidenebis(3-methyl-6-t-butylphenol),3,9-bis[1,1-dimethyl-2-O-(3-t-butyl-4-hydroxy-5-methyl-phenyl)propionyloxy)ethyl]-2,4,8,10-tetraoxaspiro[5.5]-undecane,1,1,3-tris(2-methyl-4-hydroxy-5-t-butylphenyl)butane, and1,3,5-trimethyl-2,4,6-tris(3,5-di-t-butyl-4-hydroxybenzyl)-benzene.Inter alia, 2,6-di-t-butyl-p-cresol is preferred.

Examples of phosphorus based antioxidants include triphenyl phosphite,diphenyl alkyl phosphites, phenyl dialkyl phosphites, tri(nonylphenyl)phosphite, trilauryl phosphite, trioctadecyl phosphite, distearylpentaerythritol diphosphite, tris(2,4-di-tert-butylphenyl)phosphite,diisodecyl pentaerythritol diphosphite, di(2,4-di-tert-butylphenyl)pentaerythritol diphosphite, tristearyl sorbitol triphosphite, andtetrakis(2,4-di-tert-butylphenyl)-4,4′-biphenyl diphosphonate. Interalia, triphenyl phosphite is preferred.

Examples of sulfur based antioxidants includedilauryl-3,3′-thiodipropionate, dimyristyl-3,3′-thiodipropionate, anddistearyl-3,3′-thiodipropionate.

These antioxidants may be used alone. Preferably a phosphorus basedantioxidant is used alone, or a phenol based antioxidant and aphosphorus based antioxidant are used in combination. In this regard,the phenol based antioxidant and the phosphorus based antioxidant areused in such a proportion that a weight ratio of phenol basedantioxidant to phosphorus based antioxidant is in the range from 0:100to 70:30, and more preferably from 0:100 to 50:50.

The antioxidant is preferably compounded in an amount of 0.01 to 10parts, and more preferably 0.03 to 5 parts by weight per 100 parts byweight of the epoxy resin composition. Too less an amount of theantioxidant may fail to achieve sufficient heat resistance and allow fordiscoloration. Too much the antioxidant may become cure-inhibitory,failing to acquire sufficient cure and strength.

D. Curing Catalyst

Component (D) is a curing catalyst which may be selected from well-knowncuring catalysts used in epoxy resin compositions. Exemplary curingcatalysts include, but are not limited to, tertiary amines, imidazoles,and organic carboxylic acid salts thereof, organic carboxylic acid metalsalts, metal-organic chelate compounds, aromatic sulfonium salts,organic phosphine compounds, and salts thereof, which may be used aloneor in admixture. Of these, imidazoles and phosphorus based curingcatalysts are more preferred, for example, 2-ethyl-4-methylimidazole,methyl-tributylphosphonium-dimethyl phosphate, and quaternaryphosphonium bromide.

The cure accelerator is preferably used in an amount of 0.05 to 5%, andmore preferably 0.1 to 2% by weight based on the entire composition.Outside the range, the cured product of the epoxy resin composition maylose a balance of heat resistance and moisture resistance.

In the practice of the invention, components (A), (B) and (C) should bepreviously melt mixed at 70 to 120° C., preferably 80 to 110° C., toform a solid material having a softening point of 50 to 100° C.,preferably 60 to 90° C., and the solid material be ground prior tocompounding. If the material obtained by melt mixing has a softeningpoint below 50° C., it does not become solid. A softening point above100° C. leads to a loss of flow.

In a more preferred embodiment, the triazine derived epoxy resin (A-1)is used alone as component (A), components (A-1) and (B), preferablycomponents (A-1), (B) and (C) are previously reacted at 70 to 120° C.,preferably 80 to 110° C., for 4 to 20 hours, preferably 6 to 15 hours,or components (A-1), (B) and (D), preferably components (A-1), (B), (C)and (D) are previously reacted at 30 to 80° C., preferably 40 to 60° C.,for 10 to 72 hours, preferably 36 to 60 hours, to form a solid materialhaving a softening point of 50 to 100° C., and preferably 60 to 90° C.,and the solid material is ground prior to compounding. If the materialresulting from reaction has a softening point below 50° C., it may notbecome solid. A softening point above 100° C. may lead to a loss offlow.

In the preferred embodiment, if the reaction time is too short, thematerial may not become solid due to a low content of high molecularweight fraction. If the reaction time is too long, the flow may becomeless.

The solid reaction product obtained herein is preferably the reactionproduct of the triazine derived epoxy resin as component (A) with theacid anhydride as component (B), which contains a high molecular weightfraction having a molecular weight of more than 1500, a moderatemolecular weight fraction having a molecular weight of 300 to 1500, anda monomeric fraction, as analyzed by gel permeation chromatography (GPC)(under analytical conditions: sample concentration 0.2 wt %, feed volume50 μL, mobile phase THF 100%, flow rate 1.0 mL/min, temperature 40° C.,and a detector RI), wherein 20 to 70% by weight of the high molecularweight fraction, 10 to 60% by weight of the moderate molecular weightfraction, and 10 to 40% by weight of the monomeric fraction are present.

In the embodiment wherein triglycidyl isocyanate is used as component(A), the solid reaction product mentioned above contains a reactionproduct represented by the following formula (2), and especially areaction product represented by the following formula (3) when the acidanhydride as component (B) is methylhexahydrophthalic anhydride.

In the formulae, R is an acid anhydride residue, and n is an arbitrarynumber in the range of 0 to 200. The reaction product has an averagemolecular weight of 500 to 100,000. The solid reaction product accordingto the invention preferably contains 20 to 70%, especially 30 to 60% byweight of a high molecular weight fraction with a molecular weight ofmore than 1500, 10 to 60%, especially 10 to 40% by weight of a moderatemolecular weight fraction with a molecular weight of 300 to 1500, and 10to 40%, especially 15 to 30% by weight of a monomeric fraction(unreacted epoxy resin and acid anhydride).

The epoxy resin composition of the invention contains the resincomponent obtained by the above-mentioned procedure. If the antioxidant(C) and the curing catalyst (D) are not used during the preparation ofthe resin component, the antioxidant (C) and the curing catalyst (D) arepreferably compounded with the resin component at the stage when theepoxy resin composition is prepared.

In the epoxy resin composition, the following components may be furthercompounded.

E. Reflective Member

For the reflective member as component (E), titanium dioxide isespecially preferred, although barium titanate, zinc oxide and the likemay also be used. Titanium dioxide is compounded as a white colorant forenhancing whiteness and has a unit lattice which may be either rutile oranatase type. It is not limited in average particle size and shape. Thetitanium dioxide may be previously surface treated with hydrous oxidesof aluminum, silicon or the like for enhancing its compatibility withand dispersibility in resins and inorganic fillers.

An amount of titanium dioxide loaded is preferably 2 to 80% by weightand more preferably 5 to 50% by weight of the entire composition. Lessthan 2% by weight may fail to achieve a sufficient whiteness whereasmore than 80% by weight may adversely affect molding properties, leavingunfilled or void defects.

F. Inorganic Filler

For the inorganic filler as component (F), any fillers other thancomponent (E) commonly compounded in epoxy resin compositions may beused. Examples include silicas such as fused silica and crystallinesilica, alumina, silicon nitride, aluminum nitride, boron nitride, glassfibers, and antimony trioxide. These inorganic fillers are notparticularly limited in average particle size and shape.

The inorganic filler which has been surface treated with coupling agentssuch as silane coupling agents and titanate coupling agents may becompounded for enhancing the bond strength between the resin and theinorganic filler.

Suitable and preferable coupling agents include, for example, epoxyfunctional alkoxysilanes such as γ-glycidoxypropyltrimethoxysilane,γ-glycidoxypropylmethyldiethoxysilane, andβ-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, amino functionalalkoxysilanes such as N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane,γ-aminopropyltriethoxysilane, andN-phenyl-γ-aminopropyltrimethoxysilane, and mercapto functionalalkoxysilanes such as γ-mercaptopropyltrimethoxysilane. It is understoodthat the amount of the coupling agent used for surface treatment and thesurface treatment technique are not particularly limited.

An amount of the inorganic filler added is preferably 20 to 700 parts byweight and more preferably 50 to 400 parts by weight per 100 parts byweight of the epoxy resin (A) and the acid anhydride (B) combined. Lessthan 20 pbw may fail to achieve a sufficient strength whereas more than700 pbw may result in unfilled defects due to a viscosity buildup andfailures such as separation within the device or package due to a lossof flexibility. The inorganic filler is preferably contained in anamount of 10 to 90% by weight and more preferably 20 to 80% by weightbased on the entire composition.

Other Additives

In the epoxy resin composition of the invention, various additives maybe compounded if necessary. For example, various stress-reducing agentssuch as thermoplastic resins, thermoplastic elastomers, organicsynthetic rubbers and silicones, waxes, halogen trapping agents, andother additives may be added and compounded for the purpose of improvingcertain properties of the resin insofar as this does not compromise theeffects of the invention.

Preparation of Epoxy Resin Composition

The epoxy resin composition of the invention is prepared as a moldingcompound, preferably by previously combining components (A), (B) and (C)together, uniformly melt mixing them at a temperature in the range of 70to 120° C., and preferably 80 to 110° C. on a suitable equipment such asa solventless reactor which can be heated, until the mixture undergoes aviscosity buildup to reach a softening point sufficient to handle atroom temperature, specifically of 50 to 100° C. and preferably 60 to 90°C., then cooling the mixture into a solid mixture. It is noted thatwhere components (A-1), (B) and (D), or components (A-1), (B), (C) and(D) are used, these components are preferably combined and reacted at atemperature of 30 to 80° C., more preferably 40 to 60° C. as in theforegoing procedure.

With respect to the temperature range where the selected components aremixed in these embodiments, if the mixing temperature is too low, itfails to form a mixture which becomes solid at room temperature. If themixing temperature is too high, too high a reaction rate makes itdifficult to terminate the reaction at the desired extent of reaction.

Next, the mixture is ground, following which components (E) and (F) andother additives are compounded in predetermined formulation ratios. Theresulting mixture is fully uniformly mixed on a mixer or the like, thenmelt mixed on a hot roll mill, kneader or extruder, cooled forsolidification, and comminuted into a suitable size. The resulting epoxyresin composition is ready for use as molding compound.

The white epoxy resin composition of the invention thus obtained may beadvantageously utilized as molded parts in semiconductor and electronicequipment, especially using light-emitting elements, or encapsulants forlight-emitting elements and other semiconductor devices. Excluded arelight-sensing elements and photo-couplers having light-emitting andsensing elements integrated.

The encapsulation method which is most generally used in thisapplication is low-pressure transfer molding. Notably, the epoxy resincomposition of the invention is desirably molded at a temperature of 150to 185° C. for 30 to 180 seconds. Post-cure may be effected at 150 to195° C. for 2 to 20 hours.

Light-Emitting Element

The light-emitting element 10 used herein should have an emission peakwavelength of 430 nm or longer because the molded part 40 exhibits ahigh reflectance and possesses light resistance at or above thatwavelength. Use of a gallium nitride compound semiconductor isparticularly preferred. A light-emitting device of the prior artconstruction that a light-emitting element comprising a gallium nitridecompound semiconductor is disposed on a molded part of PPS has theproblem that the molded part can be degraded by the heat release fromthe light-emitting element because the light-emitting elements ofgallium nitride compound semiconductor produce more amounts of heat uponelectric current conduction than light-emitting elements of GaP, GaAs orthe like. The light-emitting element 10 of gallium nitride compoundsemiconductor used herein is prepared by depositing a semiconductor suchas GaN, InGaN, or InAlGaN on a substrate to form a light-emitting layer.

Sealing Member

The sealing member 50 is preferably formed using an epoxy resinincluding a triazine derived epoxy resin or a silicon-containing resinas typified by a silicone resin.

The sealing member 50 using an epoxy resin including a triazine derivedepoxy resin offers enhanced adhesion since it is of the same materialsystem as the molded part 40. Since the light-emitting element 10 ofgallium nitride compound semiconductor reaches a temperature of at least100° C. upon electric current conduction, both the sealing member 50 andthe molded part 40 are thermally expanded, though to a slight extent.When the sealing member 50 and the molded part 40 are formed ofmaterials of the same system, they have approximate coefficients ofthermal expansion so that little separation occurs at the interfacebetween the sealing member 50 and the molded part 40.

While most sealing members using silicon-containing resins tend to beless adherent to prior art molded parts using thermoplastic resins,their adhesion can be increased when the molded part 40 is made of theepoxy resin composition of the invention. Since the light-emittingelement 10 of gallium nitride compound semiconductor emits blue lighthaving a high level of emission energy upon electric currentapplication, the sealing member in close contact with the light-emittingelement 10 is most prone to degradation. The rate of degradation can beminimized by forming the sealing member from silicon-containing resins,typically silicone resins. Similarly, although the surface of the moldedpart 40, that is, its adhesion interface to the sealing member 50 isalso degraded by light and has a likelihood of separation, the adhesioninterface between the sealing member of light resistantsilicon-containing resin and the molded part of the inventive epoxyresin composition is least prone to failure.

Also, the sealing member 50 used herein may be a member formed from acured product of a thermosetting epoxy resin composition comprising (A)an epoxy resin including a triazine derived epoxy resin, (B) an acidanhydride, (C) an antioxidant, and (D) a curing catalyst, whereincomponents (A), (B) and (C) are compounded as a solid material in groundform obtained by previously melt mixing components (A), (B) and (C) at70 to 120° C. to form a solid mixture having a softening point of 50 to100° C. and grinding the mixture.

Phosphor

The phosphor 70 may be any of compounds which absorb light from thelight-emitting element 10 and wavelength convert it into light of adifferent wavelength. Use may be made of, for example, rare earth basedaluminate salt phosphors activated mainly with a lanthanoid element likeCe, such as represented by Y₃Al₅O₁₂:Ce, (Y,Gd)₃Al₅O₁₂:Ce, andY₃(Al,Ga)₅O₁₂:Ce.

EXAMPLE

Examples and Comparative Examples are given below for furtherillustrating the invention although the invention is not limited tothese Examples.

Examples 1 to 10

Of the components shown in Table 1, the epoxy resin, acid anhydride andantioxidant were previously melt mixed on a reactor at 100° C. for 3hours. The mixture was cooled for solidification (softening point 60°C.), ground, and thereafter compounded with other components in thepredetermined compositional ratio. This was uniformly melt mixed on ahot twin-roll mill, cooled, and ground, yielding a cured product of awhite epoxy resin composition serving as a molded part for use in alight-emitting device. The starting materials used herein are describedbelow.

-   (A) Epoxy resin

(A-1) Triazine derived epoxy resin

-   -   (i) Tris(2,3-epoxypropyl) isocyanate (trade name TEPIC-S by        Nissan Chemical Industries, Ltd., epoxy equivalent 100)

(A-2) Hydrogenated epoxy resin

-   -   (ii) Hydrogenated bisphenol A type epoxy resin (trade name        YL-7170 by Japan Epoxy Resins Co., Ltd., epoxy equivalent 1200)    -   (iii) Hydrogenated biphenyl type epoxy resin (trade name YL-7040        by Japan Epoxy Resins Co., Ltd., epoxy equivalent 220)

(A-3) Other aromatic epoxy resin

-   -   (iv) Bisphenol A type epoxy resin (trade name E1004 by Japan        Epoxy Resins Co., Ltd., epoxy equivalent 890)

-   (B) Acid anhydride    -   (v) Carbon-carbon double bond-free acid anhydride,        methylhexahydrophthalic anhydride (trade name Rikacid MH by New        Japan Chemical Co., Ltd.)    -   (vi) Carbon-carbon double bond-bearing acid anhydride,        tetrahydrophthalic anhydride (trade name Rikacid TH by New Japan        Chemical Co., Ltd.)    -   (vii) Phenol novolac resin (trade name TD-2131 by Dainippon Ink        & Chemicals, Inc.)

-   (C) Antioxidant    -   (viii) Phosphorus-based antioxidant: triphenyl phosphite (trade        name by Wako Pure Chemical Industries, Ltd.)    -   (ix) Phenol-based antioxidant: 2,6-di-t-butyl-p-cresol (trade        name BHT by Wako Pure Chemical Industries, Ltd.)

-   (D) Titanium dioxide, rutile type (trade name Tipaque CR-90 by    Ishihara Sangyo Kaisha Ltd.)

-   (E) Inorganic filler: ground fused silica (trade name by Tatsumori    K.K.)

-   (F) Curing catalyst    -   (x) Phosphorus-based curing catalyst:        methyl-tributyl-phosphonium-dimethyl phosphate (trade name PX-4        MP by Nippon Chemical Industrial Co., Ltd.)    -   (xi) Imidazole catalyst: 2-ethyl-4-methylimidazole (trade name        2E4MZ by Shikoku Chemicals Corp.)

These compositions were measured for the following properties. Theresults are shown in Table 1.

Spiral Flow

Using a mold according to EMMI standards, a spiral flow was measured at175° C. and 6.9 N/mm² for a molding time of 120 seconds.

Melt Viscosity

Using a constant-load orifice type flow tester with a nozzle having adiameter of 1 mm, a viscosity was measured at a temperature of 175° C.and a load of 10 kgf.

Flexural Strength

A cured part was formed at 175° C. and 6.9 N/mm² for a molding time of120 seconds using a mold according to EMMI standards, and measured forflexural strength according to JIS K-6911.

Heat Resistance or Yellowing

A disk having a diameter of 50 mm and a thickness of 3 mm was molded at175° C. and 6.9 N/mm² for a molding time of 2 minutes and allowed tostand at 180° C. for 24 hours, after which yellowness was compared.

TABLE 1 Formulation Example (pbw) 1 2 3 4 5 6 7 8 9 10 (A) A-1 (i) 9 9 84 6 9 2 A-2 (ii) 3 11 71 20 (iii) 6 A-3 (iv) 20 21 (B) Acid (v) 14 14 128 12 14 5 3 anhydride (vi) 3 Phenolic (vii) 2 resin (C) Antioxidant(viii) 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 (ix) 0.1 0.1 0.1 0.1 0.1 0.10.1 Premixing of (A) + (B) + (C) Yes Yes Yes Yes Yes No No Yes Yes Yes(D) Curing (x) 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 catalyst (xi) 0.1 0.1 (E)Titanium dioxide 6 6 6 6 6 6 6 6 6 6 (F) Inorganic filler 70 70 70 70 7070 70 70 70 70 Test Spiral flow, inch 15 25 20 18 20 15 15 25 18 17results Melt viscosity, 80 60 90 100 80 80 120 90 100 120 Pa − sFlexural strength, 100 110 150 180 120 80 150 60 90 160 N/mm² Heatresistance white white white white white light light yellow yellow paleor Yellowing yellow yellow yellow

Examples 1 to 5 wherein components (A), (B) and (C) were premixed areimproved in many properties over Examples 6 and 7 wherein they were notpremixed. Examples 1 to 5 wherein component (B) is an acid anhydridewhich is non-aromatic and free of a carbon-carbon double bond areimproved in many properties over Example 8 wherein component (B) has acarbon-carbon double bond. Examples 1 to 5 using component (A-1) and/or(A-2) are improved in many properties over Examples 9 and 10 usingcomponent (A-3). Examples 1 to 5 remain white in the heat resistance oryellowing test whereas Examples 6 to 10 yellow. Therefore, Examples 1 to5 are highly heat resistant and their molded parts are found undegraded.

Reflectance

A reflectance of a molded part is measured by Irradiating light of apredetermined wavelength thereto. FIG. 3 is a diagram showing areflectance of a molded part.

It is seen that the molded part exhibits a very high reflectance tolight having wavelengths of 430 nm or longer.

Example 11

Example 11 demonstrates a light-emitting device. In the light-emittingdevice of Example 11, an epoxy resin composition according to theinvention is molded to form a molded part on a leadframe of copper alloyby a transfer molding technique. The molded part is provided with arecess having bottom and side surfaces. A light-emitting element of blueemission comprising a sapphire substrate and a light-emitting layer ofInGaN is mounted using an epoxy resin adhesive. The light-emittingelement is electrically connected to the leadframe using gold wireshaving a diameter of 30 μm. A sealing member is applied dropwise intothe molded part with the recess on the bottom surface of which thelight-emitting element is mounted. The sealing member used contains 100parts by weight of a silicone resin, 30 parts by weight of a YAGphosphor, and 5 parts by weight of a light diffuser of silicon oxide. Itis heated from room temperature to 150° C. over 3 hours, and cured at150° C. for 5 hours. Finally, the frame is cut out, yielding alight-emitting device of white emission.

Comparative Example 1

Comparative Example 1 demonstrates a light-emitting device. In thelight-emitting device of Comparative Example 1, polyphenylene sulfide(PPS) is molded to form a molded part on a leadframe of copper alloy byinjection molding. The shape of the molded part is substantially thesame as in Example 11. A light-emitting element of blue emissioncomprising a sapphire substrate and a light-emitting layer of InGaN ismounted using an epoxy resin adhesive. The light-emitting element iselectrically connected to the leadframe using gold wires having adiameter of 30 μm. A sealing member is applied dropwise into the moldedpart with the recess on the bottom surface of which the light-emittingelement is mounted. The sealing member used contains 100 parts by weightof a silicone resin, 30 parts by weight of a YAG phosphor, and 5 partsby weight of a light diffuser of silicon oxide. It is heated from roomtemperature to 150° C. over 3 hours, and cured at 150° C. for 5 hours.Finally, the frame is cut out, yielding a light-emitting device of whiteemission.

Comparison Test

The light-emitting devices of Example 11 and Comparative Example 1 werecompared for performance and outer appearance when a current flow of 150mA was conducted for 500 hours at room temperature.

TABLE 2 Relative Separation between molded Light-emitting device output(%) part and sealing member (%) Example 11 100 0 Comparative Example 130 100

The relative output (%) is an output after 500-hour current conductionrelative to an output before current conduction which is 100%. Therelative output is determined by measuring five samples for each ofExample 11 and Comparative Example 1 and calculating an average thereof.The percent separation (or delamination) between molded part and sealingmember is 0% when no separation occurred, and 100% when separationoccurred along the entire interface. The separation between molded partand sealing member is reported when any separation is detectable even ata part of the interface between the molded part and the sealing member.The percent separation indicates the number of separated samples among100 samples prepared for each of Example 11 and Comparative Example 1.

It is thus seen that Example 11 is substantially better in heatresistance, light resistance and adhesion than Comparative Example 1.

Examples 12 to 15

An epoxy resin composition was prepared by melt mixing the reactivecomponents selected from the components shown in Table 3 under theconditions shown in Table 3, grinding the solid reaction product thusobtained, and compounding it with the remaining components.

The solid reaction product and the cured product obtained by curing theepoxy resin composition on a transfer molding machine were examined forproperties by the following methods. The results are also shown in Table3.

Solid Reaction Product

The solid reaction product was analyzed by GPC under the followingconditions. Using a chromatograph HLC-8120 (Tosoh Corp.) equipped withTSK guard columns HXL-L+G4, 3, 2, 2HxL, analysis was performed underconditions: a sample concentration 0.2%, a feed volume 50 μl, a mobilephase THF 100%, a flow rate 1.0 mL/min, a temperature 40° C., and adetector RI.

From the GPC analysis data, the ratios of TEPIC monomer, MH monomer,moderate molecular weight fraction, and high molecular weight fractionwere computed. The fraction ratio values in Table 3 are by weight.

TEPIC-S monomer: one area having a peak at 37.3±0.5 minutes

MH monomer: one area having a peak at 38.3±0.5 minutes

moderate molecular weight fraction: area ranging from 30.8 to 36.8minutes

high molecular weight fraction: area ranging from 0 to 30.7 minutes

Evaluation of Composition

The composition was examined and evaluated for gel time, yellowing,thermogravimetric-differential thermal analysis (TG-DTA) and strength.

Gel Time:

A sample, 1.0 g, was placed on a hot plate at 175° C., and at the sametime measurement was started with a stopwatch. The sample on the hotplate was scraped, detecting the time when the sample started gelation.

Yellowing:

A sample, 10 g, was cured in an aluminum dish at 180° C. for 60 seconds,after which it was examined for yellowing. The cured sample was held at180° C. for 24 hours, after which it was examined for yellowing again.

Rating

⊚ (excellent) clear, colorless ◯ (good) light yellow Δ (fair) lightbrown X (poor) brown

TG-DTA:

Analysis was performed by molding a sample at 180° C. for 60 secondsinto a disc specimen having a diameter of 10 mm and a height of 2 mm,heating at a rate of 5° C./min from room temperature to 500° C.,obtaining a thermogravimetric curve, and determining the temperaturecorresponding to a weight loss of 0.2% from the curve.

Strength:

A sample was molded at 180° C. for 60 seconds into a specimen of50×10×0.5 mm. Three-point flexural strength was measured at roomtemperature and a test speed of 2 mm/sec.

TABLE 3 Example Example Example Example Component (pbw) 12 13 14 15Pre-mixing TEPIC-S 45 45 45 45 MH 55 55 55 55 Triphenyl phosphite 3 32E4MZ 1 Molar ratio of epoxy/ 1.4 1.4 1.4 1.4 acid anhydride in premixReaction conditions 80° C./ 80° C./ 80° C./ 40° C./ 10 hr 10 hr 10 hr 48hr Post-mixing Triphenyl phosphite 3 3 2E4MZ 1 1 U-CAT 5003* 2 GPC dataof solid reaction product MH monomer ratio 9.5 7.1 10.8 8.4 TEPICmonomer ratio 16.5 13.3 16.4 19.0 Moderate MW fraction 16.2 17.3 16.345.4 High MW fraction 51.6 53.8 49.0 21.6 Cured properties Gel time(sec) 8 8 9 22 Yellowing as cured at 180° C. ⊚ ⊚ ⊚ ⊚ after 180° C./24 hr◯ ⊚ ⊚ ◯ TG-DTA 290° C. 295° C. 285° C. 260° C. Strength 8.4 8.4 7.5 8.2*phosphorus-based curing catalyst: quaternary phosphonium bromide (tradename U-CAT 5003 by San-Apro, Ltd.)

It is noted that the solid reaction products of Examples 12 to 15contain a compound having the following formula with a molecular weightof more than 1,500, a compound having the following formula with amolecular weight of 300-1,500, and the monomers in proportions X, Y, andZ (expressed by weight), respectively.

Solid reaction product of Example 12

-   -   X=51.6 Y=16.2 Z=27.0

Solid reaction product of Example 13

-   -   X=53.8 Y=17.3 Z=20.4

Solid reaction product of Example 14

-   -   X=49.0 Y=16.3 Z=27.2

Solid reaction product of Example 15

-   -   X=23.8 Y=58.3 Z=10.2

It is noted that although compositions which have not been B-staged areapplicable in some cases, B-staged compositions are preferred in thepractice of the invention. This is because B-staged compositions arehard to yellow and maintain a high strength.

INDUSTRIAL APPLICABILITY

The light-emitting device of the invention can be utilized asluminaires, displays, mobile phone backlights, moving pictureilluminating auxiliary light sources, and other general commercial lightsources.

1-20. (canceled)
 21. A method for preparing a light-emitting devicecomprising the first step of reacting (A) a triazine derived epoxy resinselected from the group consisting of tris(2,3-epoxypropyl)isocyanurateand tris(α-methylglycidyl)isocyanurate with (B) an acid anhydride insuch a proportion as to provide an epoxy group equivalent/acid anhydridegroup equivalent ratio from 0.6 to 2.0 in the presence of (C) anantioxidant thereby obtaining a solid reaction product, and grinding thesolid reaction product, the second step of mixing a solid material inground resulting from the first step with (D) a curing catalyst, (E) areflective member, and (F) an inorganic filler, the third step ofmolding a thermosetting epoxy resin composition resulting from the firstand second steps in a mold with leads arranged in place by a transfermolding technique, and the fourth step of disposing a light-emittingelement on the leads on a cured product of the thermosetting epoxy resincomposition resulting from the third step.
 22. The method of claim 21,wherein components (A), (B) and (C) are previously reacted at 70 to 120°C. for 4 to 20 hours, thereby forming a solid material having asoftening point of 50 to 100° C., and the solid material is ground priorto compounding.
 23. A method for preparing a light-emitting devicecomprising the first step of reacting (A) a triazine derived epoxy resinselected from the group consisting of tris(2,3-epoxypropyl)isocyanurateand tris(α-methylglycidyl)isocyanurate with (B) an acid anhydride insuch a proportion as to provide an epoxy group equivalent/acid anhydridegroup equivalent ratio from 0.6 to 2.0 in the presences of both (C) anantioxidant and (D) a curing catalyst thereby obtaining a solid reactionproduct, and grinding the solid reaction product, the second step ofmixing a solid material in ground resulting from the first step with (D)a curing catalyst, (E) a reflective member, and (F) an inorganic filler,the third step of molding a thermosetting epoxy resin compositionresulting from the first and second steps in a mold with leads arrangedin place by a transfer molding technique, and the fourth step ofdisposing a light-emitting element on the leads on a cured product ofthe thermosetting epoxy resin composition resulting from the third step.24. The method of claim 23, wherein components (A), (B), (C) and (D) arepreviously reacted at 30 to 80° C. for 10 to 72 hours, thereby forming asolid material having a softening point of 50 to 100° C., and the solidmaterial is ground prior to compounding.